Mangiferin inhibits cGAS-STING pathway-related inflammation via Nrf2 activation to protect against sepsis-induced heart injury.

BACKGROUND: Septic cardiomyopathy is characterized by oxidative stress and inflammation, and accounts for its associated high mortality. Mangiferin is a naturally occurring xanthonoid found abundantly in Anemarrhena asphodeloides Bunge, a traditional Chinese herb widely used for treatment of cardiovascular diseases. This study was designed to investigate the cardioprotective role of mangiferin against sepsis-induced heart injury with a focus on mitochondrial DNA (mtDNA) release and cGAS-STING pathway-related inflammation. METHODS: The septic cardiomyopathy model in mice was established by intraperitoneal injection of LPS (10 mg/kg). Cardiac Nrf2 in septic mice was knocked down with AAV9-CTNT-Nrf2 shRNA to confirm the activity of mangiferin. Cardiomyocytes were cultured with LPS for further in vitro studies. RESULTS: Oral administration of mangiferin enhanced the survival of mice against endotoxin-induced insult. When LPS challenge impaired cardiac structural integrity, mangiferin reduced macrophage recruitment in the heart and inhibited the gene expression of pro-inflammatory cytokines. In the septic heart, mangiferin increased Nrf2 protein expression, thereby protecting the heart from oxidative damage. Mechanistically, mangiferin increased Nrf2 protein abundance by promoting Keap-1 degradation, which in turn prevented Nrf2 from undergoing proteasomal degradation. Unlike nuclear DNA (nDNA), mitochondrial DNA (mtDNA) acts as a ligand to induce toll-like receptor (TLR) activation once released into the cytoplasm. By protecting mitochondrial membrane integrity, mangiferin combated oxidative stress to prevent mitochondrial fragmentation and prevented the opening of mitochondrial permeability transition pore (mPTP) and the collapse of mitochondrial membrane potential in a manner this is dependent on Nrf2 availability. These effects were, however, blocked in the presence of a special Nrf2 inhibitor, ML385. Similar to TLR4, TLR9 is a member of the damage-associated molecular patterns (DAMPs). It can induce immune response through STING/IRF3 signaling. In septic mouse heart, mangiferin inhibited cGAS activity, deactivated STING/IRF3 signaling via dephosphorylation and resultantly suppressed interferon response due to limited mtDNA leakage. In cultured cardiomyocytes, mangiferin blocked STING/IRF3 signaling cascades in a Nrf2-dependent manner. Cardiac knockdown of Nrf2 with AAV9-CTNT-Nrf2 shRNA in septic mice demonstrated that Nrf2 deficiency diminished the inhibitory effects of mangiferin on cGAS-STING pathway-related inflammation. CONCLUSION: Through Nrf2 activation, mangiferin ameliorates mitochondrial dysfunction to block mtDNA release and subsequent cGAS-STING pathway-related inflammation, resultantly protecting the heart against septic insult. These events suggest the potential in the treatment of heart injury from the perspective of mitochondrial protection.